I just found out about SOLAS lifeboat bags. Not being a boater I've not ever been much interested in survival at sea but I've discovered these today as somebody local has a couple of the Mk1 going for $20-
www.hansenprotection.no
If the seller gets back to me I'll buy the 2 she has. mainly because that would be cheaper than a heavy duty space blanket and/or the non-breathable SOL bivvy shelter. So...
New thought on the "Survival" bag

Ascotherm Mk I - raft suit / thermal protective aid TPA
Ascotherm Mk I - The original TPA
New thought on the "Survival" bag